Internal combustion engines

ABSTRACT

Pressure charging apparatus, which may be a turbocharger or a supercharger, for an internal combustion engine comprises a pressure supply, a wastegate, a wastegate actuator for closing and opening the wastegate in order to alter the pressure in the engine inlet, a boost control for controlling the wastegate actuator, a boost control solenoid valve, a switchover valve, electronic control units and a full throttle sensor. In operation, unit receives signals, inter alia, from the sensor to control valves to positively shut the wastegate until an overboost threshold is reached thereby minimizing boost lag during this period.

This is a continuation of application Ser. No. 08/331,616, filed on Nov.3, 1994, which was abandoned upon the filing hereof.

FIELD OF THE INVENTION

The present invention relates to pressure charging apparatus forinternal combustion engines.

BACKGROUND AND SUMMARY OF THE INVENTION

The pressure charging apparatus may be a turbocharger or a superchargerin which, typically, in one known arrangement, engine boost level iscontrolled by a pneumatically controlled wastegate mechanism. The engineboost level is defined as the pressure level, relative to atmospheric,to which the turbocharger or supercharger compresses the air charge inthe inlet manifold. The wastegate position, which controls the boostlevel is in turn controlled by a controlling pneumatic pressure which isregulated by a boost control solenoid valve. The boost control solenoidvalve, which is fitted between the wastegate actuator mechanism and apressure source (or reservoir), is actuated by an electrical controlsignal. This may be in the form of a voltage, frequency or duty cycle.The boost control solenoid valve is of a type where the full supplypressure is diverted to the wastegate actuator to open it fully (causinglow engine boost) when a `low` signal is supplied to the solenoid. Thefull supply pressure is diverted to vent away and no pressure reachesthe wastegate actuator (causing high engine boost), when a `high` signalis supplied to the solenoid. The solenoid operation is infinitelyvariable between these two extremes.

The signal to the boost control solenoid valve is usually supplied froman Electrical Control Unit (ECU), which may use engine speed, boostpressure and engine load amongst the incoming parameters. This enablesthe boost pressure to be controlled as desired via the action of theboost control solenoid valve. The ECU is pre-programmed to provide thedesired boost levels dependent upon the incoming parameters. Additionalsafeguards may be incorporated into the inputs to the ECU, such that alow signal is sent to the boost control solenoid valve under conditionsof engine stress (vibration or combustion detonation as examples) or forreason of vehicle safety inhibits (cruise control operation, vehiclebraking and gearchange operation examples).

The existing arrangement is such that when a change is made to theelectrical signal to the boost control solenoid valve, there is a delaybefore the wastegate actuator assumes the new position. This delay isdependent upon the control dynamics of the system such as the length ofpipes and volume of the wastegate actuator and is generally engineeredto be small. Under conditions of a changing signal to the boost controlsolenoid valve, there may also be a tracking error present that is tosay the difference between the required and actual signal levels. Thismay occur under conditions of engine acceleration.

The existing arrangement does not permit the control dynamics to bealtered in response either to the nature of the inputs to the ECU or tothe state of the output from the ECU to the boost control solenoidvalve.

According to the present invention there is provided pressure chargingapparatus for internal combustion engines comprising means for supplyingair under pressure to the engine inlet, a wastegate, a wastegateactuator for closing and opening the wastegate in order to alter thepressure in the engine inlet, characterised by a boost control forcontrolling the wastegate actuator, first valve means connected to thewastegate actuator and to the boost control, and control means operativeto control the operation of second valve means in dependence, interalia, upon a signal from a full throttle sensor and thereby thewastegate actuator.

In a preferred embodiment of the invention, the means for supplying aircomprises an air compressor. The first valve means comprises a boostcontrol solenoid valve operative in one position to vent to atmosphere.The second valve means is operative to connect the wastegate actuator(on the opposing side) to the means for supplying air or to atmosphere.The boost control is programmed to operate the boost control solenoidvalve at a duty cycle which may be infinitely variable between 0 and100%. The duty cycles are advantageously 100% and 70%.

In order that the invention may be more-clearly understood, twoembodiments thereof will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 diagrammatically shows an existing internal combustion engineboost control system,

FIG. 2 diagrammatically shows an internal combustion engine boostcontrol system according to the invention,

FIG. 3a shows duty cycle plotted against engine speed for thearrangements of FIGS. 1 and 2 (that for FIG. 1 is shown in solid lineand that for FIG. 2 is shown in dotted line).

FIG. 3b shows engine inlet manifold pressures plotted against enginespeed, the pressures corresponding to the duty cycle values of FIG. 3a,for the arrangements of FIG. 1 and 2 (that for FIG. 1 is shown in solidline, that for FIG. 2 is shown in dotted line and that for steady statearrangements is shown in chain line.

FIG. 4a shows duty cycle plotted against time for the arrangements ofFIGS. 1 and 2 (that for FIG. 1 is shown in solid line and that for FIG.2 is shown in dotted line).

FIG. 4b shows engine inlet manifold pressures plotted against time forthe arrangements of FIGS. 1 and 2 (that for FIG. 1 is shown in solidline and that for FIG. 2 is shown in dotted line),

FIG. 4c shows the signal applied to a switchover valve plotted againsttime,

FIG. 5 shows a logic sequence diagram for the operation of the system ofFIG. 2,

FIG. 6 shows a logic diagram similar to FIG. 5 but for the prior artsystem of FIG. 1,

FIG. 7 shows an alternative embodiment to that of FIG. 2,

FIG, 8a shows a graph of duty cycle against time,

FIG. 8b shows a graph of switchover valve signal

FIG. 8c shows a graph of manifold boost pressure against time (allgraphs 8a, 8b and 8c under full throttle acceleration from rest for theembodiment of FIG. 7), and

FIG. 9 shows a particular form of wastegate for the embodiment of FIG.7.

FIG. 10 is a schematic illustration of the engine, wastegate, compressorand throttle used with the control of the present invention.

Referring to FIG. 1, the system comprises a boost control electroniccontrol unit (ECU) 1, a boost control solenoid valve 2 and a wastegateactuator 3. Under the control of the ECU, the solenoid controls air flowfrom an air pressure supply 4 via an air pressure line 5 and directs iteither to a vent 6 or to the wastegate actuator 3 which in turn controlsthe wastegate (not shown). The boost control ECU receives signals viathe vehicle wiring harness. These may comprise signals from knocksensors, cruise control devices, brake lights, boost pressuremeasurement devices and engine speed measurement devices.

The boost control ECU 1 contains a duty cycle "map" similar to thatshown in FIG. 3a and a boost "map" similar to that shown in FIG. 4a. Theduty cycle map values are chosen such that the resultant boost valuesachieved from the engine will be slightly higher than the boost valuescontained within the boost map. An internal function of the boostcontrol ECU 1 monitors the actual engine boost level. When the boost mapvalue is reached, it is able to moderate the duty cycle signal to theboost control solenoid valve 2. The sisal is then less than that heldwithin the duty cycle map. In response to this reduced signal, thewastegate opens further reducing the engine's capacity to produce boost.The boost level therefore falls. Once the boost level falls below theboost map value, the duty cycle signal is restored to that containedwithin the duty cycle map. This feedback system is continuous. Thematching of the actual duty cycle to achieve the boost map levels andthe values within the duty cycle map has to be made carefully. If thedifference is too great wild oscillations in engine boost level mayresult. The frill load duty cycle map referred to above has maximumvalues of about 70% in practice. Similar values at low engine loads andspeeds are near to 100%.

With the above described system, the wastegate, shown schematically withthe engine and compressor in FIG. 10 operates in the following mannerwith the engine subject to full throttle acceleration from rest. In therest condition, the engine is idling and the wastegate is fully shiftwith an electrical duty cycle signal of 100% being supplied to the boostcontrol solenoid valve 2. When full throttle is applied, the enginequickly accelerates to the torque converter (gearbox) stall speed. Atthis speed, the value within the duty cycle full load map dictates thatthe wastegate should be opening in response to a 70% duty cycle. This isa problem condition. The wastegate is open and yet the boost valuewithin the boost map has not been reached. The open wastegate isresponsible for a degree of boost lag (and poorer performance than needsbe). Once the boost level has reached the level within the boost map,the duty cycle is "moderated" as previously described. The engine isthen running at something close to the desired steady state maximumpower for the load condition. A logic sequence chart for the operationof this system is shown in FIG. 6.

It can be seen that the logic chart-allows three potential outcomes.

1) In response to any active inhibits, the boost control solenoid valvereceives a duty cycle of zero. This fully opens the wastegate, for aslong as the inhibits are active.

2) The wastegate position is constantly in a state of being altered,such that the engine boost level is controlled close to the desired`map` values. This is the `normal` steady state running condition forthe engine.

3) under conditions of continuous engine `knock` the duty cycle value`sent` to the boost control solenoid valve will eventually reduce to avalue of zero. This is not a `normal` engine running condition.

The relationship between the boost ECU, boost control solenoid valve,wastegate actuator and wastegate position may be discerned from theschematic diagram of the existing boost control arrangement.

Referring to FIG. 2, in which equivalent parts bear the same referencenumerals as in FIG. 1, the system of the invention comprises anadditional electronic control unit (ECU) 10. This occupies the positionof ECU 1 in FIG. 1 embodiment and communicates with the boost controlECU 1. Apart from the signals received by way of the vehicle wiringharness, the new ECU 10 also receives a signal from a full throttlesensor 13. The FIG. 2 system also comprises a switchover valve 11. Thisvalve 11 and the boost control solenoid valve 2 are connected to receivesignals from the new ECU 10. Airlines run from the switchover valve tothe air pressure supply 4, the boost control solenoid valve 2, and theopposing side of the wastegate actuator 3. Solenoid valve 2 also leadsto a vent 6 as in the FIG. 1 system and the switchover valve to a vent12. The wastegate actuator comprises two chambers 3a and 3b separated bya diaphragm 3c to which is connected an actuating member 3d for thewastegate itself. Chamber 3a is the positive side of the actuator andchamber 3b is the negative or opposing side of the actuator. Thediaphragm 3c is spring biassed by a compression spring 3e.

With the above described system, operation under full throttleacceleration of the engine from rest with the arrangement of FIG. 2 isas follows.

In the rest condition the engine is idling as before. The full throttlecondition has not been used in the preceding 15 seconds and the brakeinhibit is not active.

Full throttle is applied and the boost ECU 1 signal is overridden. Aduty signal of 100% is applied to the boost control solenoid valve 2. Asignal is supplied to the switchover valve in order to positively shutthe wastegate, complementing the high signal sent to the boost controlsolenoid.

The wastegate stays shut until an overboost threshold is reached--thisarrangement minimises boost lag considerations during this period.

Once the predetermined overboost threshold is reached the new ECU 10provides a 70% duty cycle for a short period of time before returningcontrol to the boost ECU 1 for the normal signal moderation control. Theshort period at 70% duty cycle Is necessary to avoid a massive boostundershoot correction on control handover.

A number of "fail safes" are incorporated into the new ECU 10, some ofwhich are listed below:

1) Circuit can only `overboost` once in any 15 second period (and notwithout backing off the throttle in the intervening period).

2) Engine detonation, cruise control and brake inhibits return controlto boost ECU.

3) Wiring fault to air pressure boost sensor will return control to theboost ECU.

4) If overboost level is not achieved within a certain time period,control reverts to boost ECU.

The logic sequence chart for the above described operation is shown inFIG. 5.

The graph of FIG. 3a shows duty cycle against engine speed for both theexisting and proposed arrangement. In this example it can be seen thatthe desired overboost pressure is reached at an engine speed of 2600 rpmand steady-state the control regained at 2750 rpm. It can be seen thatthe duty cycle values from the existing boost control system have beenoverridden from 2000 to 3600 rpm. In actual fact this system has beenoverridden from the moment of full throttle application. The examplefigures are such that the duty cycle values from the existing boostcontrol system between idle and 2000 rpm, are the same as those by whichthey are being overridden.

The graph of FIG. 3b shows engine inlet manifold pressures correspondingto the duty cycle values from the graph of FIG. 3a. In this example itcan be seen that with the existing arrangement, the actual boost valueslag the steady-state values until an engine speed of 2800 rpm. In this`lag` region, the full capabilities of the engine are not beingrealized. In the proposed arrangement the actual boost value lags onlyuntil 2250 rpm. Between 2250 and 2750 rpm. the engine is being`overboosted`, fully exploiting the engine's transient capabilities,

The graph of FIG. 4a shows duty cycle against time whereas the graph ofFIG. 4b shows the corresponding inlet manifold pressures. The graph ofFIG. 4c shows the signal supplied to the switchover valve against time.The characteristic curves are the same as for the graphs of FIGS. 3a and3b. The horizontal axes however distorted due to the flexible couplingswithin the transmission system of a real chassis.

This arrangement overcomes the prematurely opening wastegate problem. Italso exploits the engine's ability to withstand engine boost levelshigher than those steady state values for short periods of time.

The new ECU 10 can connect the prior art boost system to the controlsolenoid (using duty cycles infinitely variable between 0 and 100%) oroverride the prior art system with other duty cycles. Two values of 100%and 70% have been chosen by way of example, although a refinement of thesystem might call for more discreet steps (or variable steps) duringthis override period.

FIG. 10 illustrates the position of the wastegate 20 positioned in abypass from the exhaust from the engine 22. Theoretically, the wastegatecan be located anywhere in the air line from the compressor to theengine or from the exhaust from the engine to the turbine.

A second embodiment is shown in FIG. 7 in which parts equivalent to theembodiment of FIG. 2 bear the same reference numerals. In this secondembodiment, the additional ECU 10 receives a signal from full throttlesensor 13 and pressure sensor mounted at the inlet manifold 14. Theexisting vehicle's boost control system remains in place. An additionalswitchover valve 11 is connected to receive signals from the additionalECU 10. Air lines run from the switchover valve to the air pressuresupply 4A, and the opposing side of the wastegate actuator 3.

With the above described system, operation under full throttleacceleration of the engine from rest is as follows:

When full throttle is applied the additional ECU supplies a high signalto the switchover valve, causing a high pressure in wastegate chamber3b. Whilst the engine is accelerating up to the torque converter stallspeed, the standard boost ECU 1 supplies a high signal to the boostcontrol solenoid 2, causing a low pressure in wastegate chamber 3a. Thewastegate is therefore fully shut. Once the torque converter stall speedhas been met, the duty cycle full load map within boost control ECU 1dictates that the signal to the boost control solenoid is reduced to70%. However, since the manifold boost pressure has not yet met thepredetermined level set within the additional ECU, the high signal tothe switchover valve is retained. This is sufficient to cause thewastegate to remain shut. When the steady-state manifold boost pressureis reached, the signal supplied by the standard boost control ECU to theboost control solenoid will further begin to reduce from 70%. Thewastegate remains shut because a high signal from the additional ECUcontinues to be sent to the switchover valve. By ensuring that thepressure in wastegate chamber 3b is sufficiently high in considerationof the wastegate spring force 3e, exhaust back pressure and the pressurein wastegate chamber 3a, it is possible to ensure that a high signal atthe switchover valve will shut, the wastegate valve under all fullthrottle engine operating conditions. The standard boost control istherefore overridden. Once the predetermined overboost threshold isreached, the additional ECU reduces the signal at the switchover valvegradually, causing a controlled reduction in manifold boost pressure.When the signal at the switchover valve reaches zero, the wastegateposition is fully under the control of the signal which the standard ECUsends to the boost control solenoid. Standard operating conditions aretherefore regained.

The graphs of FIGS. 8a, 8b and 8c shows duty cycle (boost controlsolenoid), signal (switchover valve) and manifold boost pressure againsttime, under full throttle acceleration from rest.

This system has significant benefits over an integrated boost andoverboost system, in that it can easily be fitted as an addition to astandard boost control system. It is apparent that the system can beexpanded such that existing sensors employed by the standard boostcontrol system can be used. The first embodiment is one in which theexisting manifold pressure sensor and knock sensor signals are employed,in conjunction with cruise control and brake inhibits. The two ECU's maynevertheless be combined to produce a fully integrated boost controlsystem. In conjunction with control of engine fuelling and ignition, afully integrated engine management system could be envisaged.

The significance of the switchover valve is as follows:

i. It enables a quick wastegate response, by positively shutting thewastegate when maximum boost is required.

ii. It can provide system independence, whereby the existing boostcontrol system my be left in situ. This is of particular benefit to an`after market performance kit`.

iii. It enables a high degree of insensitivity to exhaust blockpressure. This is of particular importance when a `popper` type valve isused as a wastegate. FIG. 9 shows such an arrangement. In this design itis possible for exhaust gas to leak past valve guide 20 and effectivelybias the diaphragm 3c under high exhaust beck pressure conditions. Apositive pressure on the opposing side 3b of the diaphragm, controlledby the switchover valve, can ensure that this unwelcome bias pressuredoes not begin to open the wastegate when full throttle accelerationconditions would benefit from a fully shut wastegate condition.

It wall be appreciated that the above embodiments have been describedbyway of example only end that many variations are possible withoutdeparting from the scope of the invention.

I claim:
 1. A pressure charging apparatus for an internal combustionengine comprising:an exhaust gas driven turbine driving a compressor forcompressing engine intake gasses, wherein the flow of exhaust gasthrough said turbine is limited by a wastegate through which exhaustgasses may be redirected in order to bypass said turbine; a wastegateactuator for opening and closing the wastegate and biased so that thewastegate is normally closed, said wastegate actuator being controlledby pneumatic pressure at two ports such that a positive pneumaticpressure at the first port acts to open the wastegate and a positivepneumatic pressure at the second port acts to close the wastegate; afirst valve means for regulating pneumatic pressure to the first port ofsaid wastegate actuator, said first valve means being controlled by anelectronic boost control unit; a full throttle sensor for detecting fullapplication of the engine's throttle; and a second valve means forregulating pneumatic pressure to the second port of said wastegateactuator, said second valve means being controlled by an electroniccontrol unit, the electronic control unit receiving a signal from saidfull throttle sensor.
 2. Pressure charging apparatus as claimed in claim1, in which the means for supplying air comprises an air compressor (4).3. Pressure charging apparatus as claimed in claim 1, in which the firstvalve means comprises a boost control solenoid valve (2) operative inone position to vent to atmosphere.
 4. Pressure charging apparatus asclaimed in claim 3, in which the boost control (1) is programmed tooperate the boost control solenoid valve (2) at a duty cycle which maybe infinitely variable between 0 and 100%.
 5. Pressure chargingapparatus as claimed in claim 3, in which the boost control (1) isprogrammed to operate the boost control solenoid valve at a duty cycleof 100%.
 6. Pressure charging apparatus as claimed in claim 3, in whichthe boost control is programmed to operate the boost control solenoidvalve (2) at a duty cycle of 70%.
 7. Pressure charging apparatus asclaimed in claim 1, in which second valve means (11) is operative toconnect the wastegate actuator (3) to the means for supplying air or toatmosphere.
 8. Pressure charging apparatus as claimed in claim 1 inwhich said second valve means (11) comprises a switchover valve and saidboost control (1) and the control means (10) comprise a single unit andthe control means (10) are programmed to operate the switchover valvebetween an open position where air from the air supply is fed to thewastegate actuator to open the wastegate and a closed position. 9.Pressure charging apparatus as claimed in claim 8, in which the controlmeans (10) are programmed to operate the switchover valve in aninfinitely variable manner between fully closed and fully open.